The invention relates to wheelchair seats, and in particular to a reclining and tilting wheelchair seat. The invention also relates to a reclining and tilting wheelchair seat having weight-shifting capability for maintaining the stability of an occupied chair during these repositioning actions. This is accomplished by minimizing the change in the center of gravity of the occupant of the wheelchair relative to the wheelchair supporting chassis. Further, the wheelchair utilizes a bilateral linkage with a single linear actuator to synchronize the forward movement of the seat relative to the base during recline in order to achieve weight-shift. This linkage also keeps the back from torquing in response to uneven loading. Further, the wheelchair has both weight-shift recline and weight-shift tilt features. Wheelchair canes are provided which permit infinite height adjustment for accessories by providing a longitudinal mounting slot.
The market for wheelchairs is constantly changing. As the average age of the world""s population continues to increase due to advances in health care, so does the need for health care appliances such as wheelchairs to serve an aging population. Further, the health care industry constantly strives to address the needs of individuals disabled by trauma and illness. While some wheelchair users may have their needs met by basic, manually operated chairs, many other wheelchair users require chairs with increasing numbers of features including electrical locomotion, shock absorption, and more comfortable seating.
Advances in seating have included features such as upholstered seats, tilting seats and reclining seats. However, features such as tilting and reclining seats, while desirable, can also be problematic. More specifically, when the seat of an occupied wheelchair is tilted or reclined, the center of gravity of the occupant of the chair relative to the wheelchair supporting chassis changes. In many cases the occupant is unable to reposition himself or herself so as to compensate for these changes. Although prior art wheelchairs have addressed the problem of changing center of gravity for a tilting-seat, similar problems associated with reclining seats have proven more difficult to overcome.
Prior art wheelchairs have attempted to solve the changing center of gravity problem upon seat recline, primarily in one of two ways. One common way to attempt to solve this problem has been to locate the wheelchair seat forward relative to the chassis of the chair. Thus, when the occupied seat is reclined by the occupant, the risk of the entire wheelchair overturning in a rearward direction is minimized. However, locating the seat toward the front of the wheelchair places too much weight on the front casters of the chair, thereby lowering the efficiency of the wheelchair motor and making it more difficult to maneuver.
An alternate prior art mode of solving the foregoing problem has been to increase the front-to-back length of the supporting chassis of the wheelchair, and locating the seat generally in the center of that chassis. Such a structure overcomes both problems associated with locating the chair toward the front of the wheelchair chassis as described immediately above. That is, the front casters of the wheelchair are free of undue loading, and upon recline of the chair seat the rear portion of the elongated chassis prevents rearward tipping of the chair. However, such a solution causes other problems. More particularly, providing an elongated chassis on the wheelchair adds unwanted weight and expense to the chair. Moreover, the elongated chassis, due to its added weight, requires more powerful and expensive motors to move the chair. Also, such an elongated chassis causes some loss of maneuverability of the wheelchair, such as in tight spots like an entryway, when compared to wheelchairs having a more compact chassis.
Objectives of the present invention include providing a reclining seat for a wheelchair, in which the center of gravity of the occupant of the chair shifts in a frontward direction relative to the chassis of the chair to maintain the stability of the wheelchair chair as the seat reclines. The invention relates to xe2x80x9cweight shiftxe2x80x9d which is used herein to mean the repositioning of the chair members in order to maintain a relatively constant center of gravity of a hypothetical chair occupant and in turn to maintain the stability of the chair. The object of maintaining the stability of the wheelchair upon recline is met by providing a mechanism for shifting the chair seat forward in response to a backward recline of the seat back. More specifically, a curved link is provided which is connected to the back portion of the seat back and which retracts the seat back about an axis offset vertically upward from the rearward bottom edge of the seat cushion. A single linear actuator acts upon a lateral tie bar extending across the length of the seat and includes a toothed gear which engages a rack below the seat cushion to bilaterally transmit the motion of the actuator to both lateral edges of the seat cushion during the forward shifting. This bilateral effect inhibits torque which could result from uneven loading while minimizing the expense of the actuator.
Another objective of the present invention is to provide such a reclining seat for a wheelchair, in which the seat can optionally be capable of tilting. The tilting aspect is also provided with weight-shift capabilities in order to maintain the center of gravity of the occupant of the chair with regard to the supporting chassis.
This is accomplished by shifting the seat forward as the seat back and seat bottom are tilted relative to the supporting chassis. It is within the scope of the invention to provide for a rearward and/or sideways shifting of the seat relative to the chassis if this is necessary to maintain the stability of the chair. Further, the weight-shifting, tilt option is provided along, but independent of, a weight-shift, recline option.
An additional object of the invention is to provide stiffer wheelchair canes having a longitudinal slot which give the ability to mount accessories such as a ventilator tray or handles with infinite height adjustment while eliminating traditional double half clamps.
A further objective of the present invention is to provide a reclining seat for a wheelchair, which is relatively inexpensive to manufacture and maintain, relatively lightweight, and durable and reliable in use.
These objectives and advantages are obtained by the weight-shifting reclining wheelchair seat of the present invention, the general nature of which may be stated as including a reclinable back which desirably includes a back-shear feature; and a seat base frame which is projected forward an appropriate amount as the seat back is reclined. The recline mechanism may include a power actuator and a controller having a user interface. Further, the chair may include an independent seat tilt mechanism which preferably also includes a weight shift feature so as to stabilize the wheelchair during use.